2. mapview advanced controls

Source: vignettes/articles/mapview_02-advanced.Rmd

Despite the possibility to quickly plot spatial data, mapview has a set of arguments for finer control of the visualization. Depending on the object class, these are:

All types

  • map - the leaflet or mapview map to use -> default NULL
  • col.regions - the color palette for colouring raster, polygon and point areas (points are essentially circles) -> default hcl.colors with palette "Inferno" for raster data and palette "viridis" for vector data
  • at - breakpoints used for the colouring -> default NULL meaning they are calculated automatically for the range of data
  • na.color - the color for NA values -> default #BEBEBE80
  • map.types - the types of the background maps -> default CartoDB.Positron, CartoDB.DarkMatter, OpenStreetMap, Esri.WorldImagery, OpenTopoMap see here for available map types
  • alpha.regions - the opacity of raster, polygon and point fills -> default 0.8 for raster, 0.6 for polygons and 0.9 for points
  • legend - whether to add a legend to the plot -> default FALSE
  • legend.opacity - opacity of the legend -> default 1
  • verbose - whether to print additional information to the console during the rendering -> default FALSE
  • layer.name - the layer name to be used for plotting -> default depends on call. For a single object the name of the object; if zcol is supplied a combination of object name and column name; for raster stack/bricks the layer names
  • … - further arguments to be passed on to respective leaflet functions such as addRasterImage or adCircleMarkers

raster only

  • maxpixels - the maximum number of pixels to plot -> default 500k. This is used so rendering doesn’t take forever. This can also be set with mapviewOptions()
  • use.layer.names - whether to use the layer names of raster objects -> default FALSE
  • trim - should rasters be trimmed off NA values around the edges -> default TRUE

vector only

  • zcol - attribute name(s) or column number(s) in attribute table of the column(s) to be rendered -> default NULL
  • burst - whether to show all (TRUE) or only one (FALSE) layer(s) -> default FALSE
  • color - color (palette) for lines -> default hcl.colors(n, palette = "viridis")
  • alpha - opacity of the lines -> default 0.9
  • cex - circle size for point data -> default 6. This can also be used to map circle size to an attribute from the object’s attribute table by supplying either column name or number
  • lwd - line width -> default 2 for lines and points, 1 for polygons
  • label - a character vector of labels to be shown on mouseover -> default feature IDs, if zcol is set the values of zcol
  • popup - the popup function to use for the popups -> default popupTable(). See chapter on popups for further options

Here’s a few examples of how selected arguments can be used:

Adjusting color, col.regions & at

Similar to the good old spplot, arguments col.regions and at can be used for finer control of the colouring

library(mapview)
library(raster)

pal = mapviewPalette("mapviewTopoColors")

kili_data <- system.file("extdata", "kiliNDVI.tif", package = "mapview")
kiliNDVI <- stack(kili_data)
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj
## = prefer_proj): Discarded datum Unknown based on Clarke 1880 mod. ellipsoid in
## Proj4 definition
mapview(kiliNDVI[[1]], col.regions = pal(100), at = seq(-0.2, 1, 0.2), legend = TRUE)
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded ellps WGS 84 in Proj4 definition: +proj=merc +a=6378137
## +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null
## +wktext +no_defs +type=crs
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded datum World Geodetic System 1984 in Proj4 definition
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded ellps WGS 84 in Proj4 definition: +proj=merc +a=6378137
## +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null
## +wktext +no_defs +type=crs
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded datum World Geodetic System 1984 in Proj4 definition


mapview(breweries, zcol = "founded", at = seq(1400, 2200, 200), legend = TRUE)

Changing map.types

To use a different background map, use argument map.types

mapview(breweries, map.types = c("Esri.WorldShadedRelief", "OpenStreetMap.DE"), color = "grey40")

Individual layer.name(s)

To individually label the layer names use argument layer.name

mapview(list(franconia, breweries),
        layer.name = c("Franconian districts", "Franconian breweries"))

Using burst

burst can be used to plot all layers of an object

mapview(breweries, burst = TRUE)


Note how all layers are shown by default. There is a hidden argument hide which can be used to hide all layers but the first.

mapview(breweries, burst = TRUE, hide = TRUE)


When burst used together with zcol, it will produce one layer for all unique values of zcol.

library(dplyr)
library(sf)

breweries %>%
  st_intersection(franconia) %>%
  mapview(zcol = "district", burst = TRUE)
## Warning: attribute variables are assumed to be spatially constant throughout all
## geometries


Note that for a column with many values there will likely not be enough space for the layers control - we are working on a solution for this issue.

Setting point size cex

For point data the circle size can be mapped to one of the attributes (features with NA values will be shown as dots)

mapview(breweries, cex = "number.of.types")

Adjusting opacity

Opacity of lines and fills (regions) can be adjusted using arguments alpha and alpha.regions

mapview(breweries, alpha = 0)


mapview(franconia, alpha.regions = 0.2, aplha = 1)

Multiple layers

In addition to easily style maps, mapview also makes it easy to add multiple layers to a (possibly laready existing) map. This can be done either by using + or by supplying a list of objects (or both).

library(plainview)

# mapview + object
mapview(list(franconia, breweries)) + poppendorf[[5]]
## Warning in wkt(projfrom): CRS object has no comment
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded ellps WGS 84 in Proj4 definition: +proj=merc +a=6378137
## +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null
## +wktext +no_defs +type=crs
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded datum World Geodetic System 1984 in Proj4 definition
## Warning in wkt(pfrom): CRS object has no comment
## Warning in rgdal::rawTransform(projfrom, projto, nrow(xy), xy[, 1], xy[, : Using
## PROJ not WKT2 strings
## Warning in wkt(pfrom): CRS object has no comment
## Warning in rgdal::rawTransform(projfrom, projto, nrow(xy), xy[, 1], xy[, : Using
## PROJ not WKT2 strings
## Warning in rgdal::rawTransform(projto_int, projfrom, nrow(xy), xy[, 1], : Using
## PROJ not WKT2 strings
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded ellps WGS 84 in Proj4 definition: +proj=merc +a=6378137
## +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null
## +wktext +no_defs +type=crs
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded datum World Geodetic System 1984 in Proj4 definition


# mapview + mapview
mapview(franconia, zcol = "district") + mapview(breweries, zcol = "founded")


library(plainview)

# mapview w list of objects
mapview(list(breweries, franconia),
        zcol = list(NULL, "district"),
        legend = list(TRUE, FALSE),
        homebutton = list(FALSE, TRUE)) + poppendorf[[5]]
## Warning in wkt(projfrom): CRS object has no comment
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded ellps WGS 84 in Proj4 definition: +proj=merc +a=6378137
## +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null
## +wktext +no_defs +type=crs
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded datum World Geodetic System 1984 in Proj4 definition
## Warning in wkt(pfrom): CRS object has no comment
## Warning in rgdal::rawTransform(projfrom, projto, nrow(xy), xy[, 1], xy[, : Using
## PROJ not WKT2 strings
## Warning in wkt(pfrom): CRS object has no comment
## Warning in rgdal::rawTransform(projfrom, projto, nrow(xy), xy[, 1], xy[, : Using
## PROJ not WKT2 strings
## Warning in rgdal::rawTransform(projto_int, projfrom, nrow(xy), xy[, 1], : Using
## PROJ not WKT2 strings
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded ellps WGS 84 in Proj4 definition: +proj=merc +a=6378137
## +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null
## +wktext +no_defs +type=crs
## Warning in showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj =
## prefer_proj): Discarded datum World Geodetic System 1984 in Proj4 definition


m1 = mapview(franconia, zcol = "district", col.regions = c("snow", "grey", "red"))
m1 + breweries

See chapter 3. mapview options for instructions on how to set some of these styling parameters permanently.